1. Field of the Invention
This invention generally relates to transducers for inducing vibratory signals in an elastic medium such as the earth and more particularly, to an improved means for coupling the horizontally directed force of a seismic transducer into the earth.
2. Description of the Prior Art
In Applicant's prior application Ser. No. 83,070 entitled Coupling Means for Horizontal Vibrator, there is disclosed means for coupling the horizontally directed force of a seismic transducer into the earth consisting of the plurality of downwardly convergent wedge-shaped, earth-engaging cleats mounted on the transducer support. It is provided therein that the cleats are of differing depths. Also, as described in the application the convergent lateral faces of the shallower cleats are preferably less steeply sloped than those of the deeper ones. This construction permits initial penetration of hard surfaces more readily, yet prevents subsequent "bottoming out".
With horizontal movement of the vibrator the earth will be displaced and hence stressed and compacted to a greater extent against the more steeply sloping faces of the cleats described in this prior application so that in consequence the less steeply sloping faces will be less effective in pushing against the earth. This is preferable in terrain where the earth materials increase in competence with depth since the stress in the earth increases with the earth's ability to withstand such stress without tearing. The inventor has recognized, however, that in other types of terrain it may be desirable to equalize these impacting forces among the cleats while retaining other advantages of variations in depth and sharpness.
It is therefore a general object of this invention to provide an improved means of coupling the horizontally directed force of a transducer into an elastic medium such as the earth.
It is a further object of this invention to provide means for coupling the horizontally directed force of transducer into the earth wherein such force is applied with maximum efficiency to earth materials varying widely in competency.
It is yet another object of this invention to provide means for coupling the horizontally directed force of a transducer into the earth which is adapted to prevent premature decoupling or "bottoming out" of the transducer.
Other and further objects and advantages of the invention will become apparent upon consideration of the following detailed description and drawings.
In summary, in accordance with the preferred embodiment of the present invention, means are provided for coupling the energy of a horizontal vibrator into the earth comprising a plurality of downwardly convergent earth-engaging cleats dependently supported from said transducer. The cleats are in the form of inverted wedges of varying depth arranged in rows extending transversely to the direction of transducer motion, each cleat having a pair of lateral load-bearing faces converging to form a horizontal cleat edge aligned with the direction of such rows, and a pair of opposed end faces normal to the horizontal plane of such edges. The lateral cleat surfaces, with the exception of those of the deepest cleats, consist of interspersed sloping and horizontal faces, and the sloping faces of the lateral surfaces of all of the cleats including the deepest ones, are equally inclined to the vertical. Because of this stair-case contour, in composite effect the shallower cleats behave as though they were more blunt. In an alternate embodiment, the lateral faces of the deepest cleats also have a staircaselike configuration.